This invention relates to agriculture machinery for soil disinfection. In particular, the invention is concerned with such a mobile device.
Soil disinfection is a standard procedure among crop growers in agriculture industry and in large scale home gardening. The disinfection process is aimed towards extermination of soil pests such as bacteria, nematodes, viruses and insects at different growth stages, undesired seeds, fungi, weeds, etc., in an attempt to make the agricultural soil more productive and to prevent diseases from damaging or reducing the agricultural crops.
By referring to the device as mobile, it is meant that it is capable of either being self-propelled or may be towed or dragged by a suitable agricultural machine such as a tractor, etc.
The common use of organic chemicals in particular methyl bromide has now been known for a while to create severe environmental problems and it is an ever growing desire to reduce to a minimum such disinfecting methods wherein at some cases chemical disinfecting is already forbidden. Other known methods for soil disinfecting are injecting steam into the soil by suitable machinery, passing steam through suitable piping embedded in the soil, firing the soil by flame throwers and others.
U.S. Pat. No. 2,966,238 discloses a device for cultivating and disinfecting a discreet portion of soil in one continuous operation, where disinfection is achieved by the use of chemicals and the soil is heated while elevated on the conveyor.
U.S. Pat. No. 2,986,841 describes a mobile earth treating apparatus wherein earth is scraped and broken up and then thrown up while being subjected to the effect of a spraying device or a flame thrower.
U.S. Pat. No. 5,553,414 discloses a mobile device for destroying soil borne pests, the device comprising a lift for raising soil from the ground, a drum in which the soil is heated and a discharger for discharging the treated soil in the ground.
U.S. Pat. No. 4,420,901 discloses a mobile device for flame treating of soil, the device comprising an elongated tube member in which the soil is conveyed by a screw-type conveyor while being flamed.
U.S. Pat. No. 5,199,212 discloses a soil decontamination system including a pulverizer and a heater volatilizing contaminants which are then burned as fuel in an internal combustion engine.
U.S. Pat. No. 5,776,422 discloses an apparatus for cleaning top soil, e.g. of a playground. The device is adapted for evenly sterilizing the soil by lifting it, passing it through the machine disinfecting it and then discharging it back.
U.S. Pat. No. 5,405,579 discloses a method for soil decontamination by passing excavated soil to a thermal treatment zone, heating the soil at super atmospheric pressure within a rotary drum, at the absence of oxygen, wherein resultant gasses pollutant steam is condensed and separated.
U.S. Pat. No. 5,176,445 discloses retrofitting asphalt production plant into a device capable of efficiently decontaminating soil.
Other patents which are in the general field of the invention are U.S. Pat. Nos. 5,188,041, 5,213,445, 5,094,012, 4,750,436, 5,499,586 and 3,802,020.
The present invention is concerned with a mobile device for disinfecting soil, avoiding the use of chemicals.
In accordance with the invention there is provided a mobile soil disinfecting device comprising a cultivating unit, a soil treating chamber, at least one bellows, at least one heat exchanger and at least one heat generating unit; the cultivating unit comprises one or more cultivating members adapted for breaking the soil and throwing it upwardly into the soil-treating chamber wherein the at least one heat exchanger is in thermal communication with the at least one heat generating unit and the at least one bellows is adapted for drawing ambient air, passing it through the at least one heat exchanger and throwing hot air into the soil treating chamber for disinfecting the soil at a suitable temperature.
The device in accordance with the present invention is suitable for cultivating soil at a variety of practical depths from about 5 to about 75 cm. This feature is of significant importance as it provides efficient disinfecting of the soil to a critical depth, this being in contrast to some of the prior art devices teaching disinfection up to a fixed depth or only of the upper layer of the soil.
The device is capable of cultivating fine layers of soil, without any additional beating or pulverizing means and typically, the cultivating members are rotatable at a speed suitable for throwing soil into the soil-treating chamber more than once at a single path of the device. In a desired mode of operation, the soil is broken into grains.
By a specific example of the present invention, the cultivating unit comprises between 3 and 48 cultivating members, usually of equal length, each being about 40 to 90 cm long. The cultivating members are fixed to a common horizontal axis rotatable at about 60 to 120 rpms. This speed range allows for loosening fine layers of soil which is spontaneously pulverized while lifted in the air. The velocity at which the device is moved along the ground surface depends, among others, on the speed of rotation of the cultivating members, the nature of soil and its humidity state, the cultivated depth etc. Typically, the velocity of the device is between 75 and 400 meters per hour.
By a preferred design of the device, the cultivating unit further comprises a surface engaging arrangement for retaining it at a fixed level above the ground surface and for overcoming obstacles. The vertical distance between the ground surface and the axis of rotation of the cultivating members may be adjusted so as to obtain varying cultivating depth.
The temperature of the air thrown into the soil treating chamber is typically in the range of between about 200xc2x0 C. and 700xc2x0 C. However, it will be appreciated that the soil is not burnt as the temperature of the warm air thrown into the cultivating chamber is adapted for destroying the pests but below the temperature burning the soil. An important feature of the present invention is that the temperature of the soil treated within the soil-treating chamber does not exceed about 15xc2x0 C. of its initial temperature, i.e. the soil does not burn. The hot air strikes the soil (preferably grains) and destroys the organisms and plant biological organisms residing in the soil.
The heat generating unit typically comprises a burner, a combustion chamber and exhaust means. The burner may be either gas or fuel operated or, in some other instances, may be also coal operated.
The temperature within the combustion chamber is in the range of about 1300xc2x0 C. and the specific heat may be in the range of about 100K to 250 K calories.
In accordance with one specific embodiment, there may be provided a preheating device. By one specific example, preheating takes place over an exhaust pipe extending through a suitable chamber or extending along the opening in the outer wall of the combustion chamber, through which air enters the heat exchanger from the bellows. In accordance with still another embodiment, the temperature of the air is gradually increased in at least two heating stages.
Furthermore, the soil does not come into contact with the burned gases of the heat generating unit. These features avoid degrading of the soil""s quality and retain fertility of the soil as compared with soil treated by prior art devices.
In addition, the device in accordance with the invention is found to be more energy saving than prior art of such devices wherein disinfecting the soil is about half the price of disinfecting the soil with a compared unit area using relevant prior art devices.
Even more so, it is an advantage of the device in accordance with the invention that after treatment, the soil is ready for use, i.e. it is already cultivated and disinfected, and there is no need for further preparations whatsoever prior to sowing.